Horizontally disposed scanning devices for scanning bar codes on articles, for instance in a supermarket, are generally known. For each article the bar codes are arranged at a determined location. In the case such a bar code is arranged on a side wall of an elongate object, it is difficult for the existing, horizontally disposed scanning devices to recognize this code. In practice the article is then tilted and the side wall is passed over the window of the scanning device.
Known from the European patent application EP-A-0 697 674 is a scanning device preferably for disposing in upright position, wherein from a rotatably disposed polygonal mirror scan lines are projected through a window via fixedly disposed mirrors directed at an angle to the vertical.
From the American patent specification U.S. Pat. No. 4,851,667 is known a scanning device for disposing in a lying position, wherein from a rotatable, polygonal mirror scan lines are projected downward onto mirrors disposed roughly horizontally and are projected therefrom out of the housing through a window via mirrors directed upward at an angle.
The present invention provides a scanning device for scanning code on an article through a window, comprising:
a source of laser light;
a rotatably drivable polygonal mirror with mirror surfaces for distributing in scan lines the laser light transmitted by the laser source; and
a number of fixedly disposed mirrors for reflecting through the window scan lines distributed by the polygonal mirror, wherein the polygonal mirror has at least one mirror surface such that in co-action with a fixedly disposed mirror at least one scan line is directed through the window at the article, which line extends for at least a moment substantially vertically to that window and the projection of which onto the article moves substantially in the plane perpendicular to that window and through that vertical line; and
a detector for receiving light scattered by the code.
Using the horizontally disposed scanning device according to the present invention it becomes possible to recognize bar codes on the articles on both the underside and standing side walls.
Further features of the present invention relate inter alia to the compact construction of such a scanning device as well as to simplified fitting thereof in flush-mounted situation in a table top.
The preferred embodiment of the device according to the present invention to be described hereinbelow is extremely compact, while a dense pattern of scan lines is projected through the window, forming part of which pattern are two substantially vertical lines. Due to a large number of mirror surfaces on the polygonal rotatable mirror, some of which lie eccentrically, or asymmetrically, relative to the optical path from the laser beam to the rotation axis of the rotatable mirror, it becomes possible to arrange in the limited space a large number of fixed mirrors which provide a large number of scan lines. The polygonal mirror, which is light in weight and preferably of injection-moulded plastic with mirror surfaces vapour-deposited thereon, is preferably driven at a high rotation speed, for instance 6000 revolutions per minute, in order to generate the diverse scan lines with a sufficiently large repetition frequency.